Deleted a large file but seeing no increase in free space or decrease of disk usage? Using UNIX or other POSIX OS?

The unlink() is not about removing file, it's about removing a file name. The manpage says: ``unlink - delete a name and possibly the file it refers to''.

Most of the time a file has just one name -- removing it will also remove (free, deallocate) the `body' of file (with one caveat, see below). That's the simple, usual case.

However, it's perfectly fine for a file to have several names (see the link() function), in the same or different directories. All the names will refer to the file body and `keep it alive', so to say. Only when all the names are removed, the body of file actually is freed.

The caveat:A file's body may *also* be `kept alive' (still using diskspace) by a process holding the file open. The body will not be deallocated (will not free disk space) as long as the process holds it open. In fact, there's a fancy way of resurrecting a file removed by a mistake but still held open by a process...

I have been working on some little tryout where a backup file was created before modifying the main textfile. Then when an error is thrown, the main file will be deleted (unlinked) and the backup file is returned instead.

Though, I have been breaking my head for about an hour on why I couldn't get my persmissions right to unlink the main file.

Finally I knew what was wrong: because I was working on the file and hadn't yet closed the file, it was still in use and ofcourse couldn't be deleted :)

So I thought of mentoining this here, to avoid others of making the same mistake:

On OSX, when fighting against a "Permission Denied" error, make sure, the directory has WRITE permissions for the executing php-user.

Furthermore, if you rely on ACLs, and want to delete a file or symlink, the containing directory needs to have "delete_child" permission in order to unlink things inside. If you only grant "delete" to the folder that will allow you to delete the container folder itself, but not the objects inside.

To anyone who's had a problem with the permissions denied error, it's sometimes caused when you try to delete a file that's in a folder higher in the hierarchy to your working directory (i.e. when trying to delete a path that starts with "../").

So to work around this problem, you can use chdir() to change the working directory to the folder where the file you want to unlink is located.

<?php $old = getcwd(); // Save the current directorychdir($path_to_file);unlink($filename);chdir($old); // Restore the old working directory ?>

This might seem obvious, but I was tearing my hair out with this problem - make sure the file you're trying to delete isn't currently being used. I had a script that was parsing a text file and was supposed to delete it after completing, but kept getting a permission denied error because I hadn't explicitly closed the file, hence it was technically still being "used" even though the parsing was complete.

ggarciaa's post above has already one small error, closedir has to be used even if $DeleteMe is false

<?php// ggarciaa at gmail dot com (04-July-2007 01:57)// I needed to empty a directory, but keeping it// so I slightly modified the contribution from// stefano at takys dot it (28-Dec-2005 11:57)// A short but powerfull recursive function// that works also if the dirs contain hidden files//// $dir = the target directory// $DeleteMe = if true delete also $dir, if false leave it alone

ggarciaa's post above has one small error, it will ignore file and directory strings that are evaluated as false (ie. "0")

Fixed code is below (false !==)

<?php// ggarciaa at gmail dot com (04-July-2007 01:57)// I needed to empty a directory, but keeping it// so I slightly modified the contribution from// stefano at takys dot it (28-Dec-2005 11:57)// A short but powerfull recursive function// that works also if the dirs contain hidden files//// $dir = the target directory// $DeleteMe = if true delete also $dir, if false leave it alone

The best way to delete files by mask is as follows:<?phparray_walk(glob('/etc/*'), 'unlink');?>Do not use array_map mentioned below - it's purpose is to process values in a given array AND COLLECT data returned by the callback function. So, array_map is slower and uses additional memory compared to array_walk.

[Editor's note: A suggestion for a work-around was submitted by argistof at gmail dot com: You can use the recursive option (see man chmod) when chmodding, for instance 'chmod 777 directory/ -R'. Be aware though, this will change the permissions of all files and folders in the diectory.]

Just a note which you probably all know, but I didn't, and it might save another poor sap some unnecessary time:

I was doing unlink() and fopen() on a file and got a permission denied error, even after chmoding the file to 0777.

The folder that contains the file must ALSO have write permission. Took a headache to find this out.

Actually you should use "@unlink" rather than testing with file_exists. The former is atomic, whereas the latter can break if you can't guarantee only one process will try to delete a given file at a time.

I know it is obvious, but.... if you have nested symlinks (for example, we archive into yyyy-mm for backups, and symbolic link to make our directory structure look flat - don't ask), unlink will only delete the top level symlink (as expected).

If you want to delete the actual file, you'll need to use readlink. If you want to delete all of the files and the symlinks, you'll need to recurse up and down to achieve that.